Modern display applications often use a backlight in combination with, for example, a transmissive liquid crystal display (LCD) layer to provide a variety of alphanumeric and/or graphical information to a viewer. For convenience of explanation such alphanumeric and/or graphical information is hereafter collectively referred to as “data” and the word “data” is intended to include all types of visually perceivable information. The most common types of backlights are fluorescent lamp backlights. While they are effective they suffer from a number of disadvantages, among which are the need for comparatively high driving voltage and the complexity or difficulty of providing dimming (variable luminescence) and user alterable color (variable chrominance). Also, in applications such as avionics systems where mechanical ruggedness is desired, the comparative fragility of fluorescent backlights can be a drawback.
It is known to use light emitting diodes (LEDs) in backlights. FIG. 1A shows a plan view and FIG. 1B shows partially cut-away side view of LED backlight 10 according to the prior art. Backlight 10 has multiple LEDs 12 mounted on printed circuit board (PCB) 14 or equivalent, with the PCB generally oriented perpendicular to backlight propagation direction 13. LEDs 12 are oriented so that principal light rays 19 emitted therefrom are coincident with, or parallel to, light 13 emitted from open surface 17 of backlight 10. Light 13 is the sum of light rays 19 emitted by individual LEDs 12. Heat sink 16 is generally provided behind PCB 14 to aid in extraction of heat generated by LEDs 12. LEDs 12 and PCB 14 are generally enclosed in box or frame 18 whose interior surfaces 11, 15 are desirably reflective and with surface 17 open. Additional optical elements such as diffusers are often placed adjacent open surface 17.
While prior art backlights such as are shown in FIGS. 1A-B are useful they often do not provide as much brightness (luminance) as is desired. This is especially troublesome in connection with head-up displays (HUDs) where the highest possible luminance is often needed. In a HUD, the data generated by the display is projected onto an angled transparent screen through which the background scene is being simultaneously viewed. The data is reflected from the angled screen toward the viewer while the background scene is transmitted through the same screen to the viewer. When the background scene is bright, the data may not be visible unless the data display is also very bright. For transmissive displays such as LCDs, the display luminance depends on the backlight luminance. Hence, there is an ongoing need for high luminance displays with high luminance backlights.
Accordingly, it is desirable to provide an improved backlight, backlit display and method, especially apparatus and methods with high luminance. In addition, it is desirable that the backlight and backlit display be simple, rugged and reliable. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.